This dataset contains the data underlying the results reported in K. Harrington et al., "An endlessly adiabatic fibre with a logarithmic refractive index distribution". The data includes the results of calculations and measurements of a fibre with a novel refractive index distribution. This includes calculated mode field diameters for various outer diameters of the fibre. Also included are optical micrographs and near-field images recorded by digital sensors and stress distributions for fibres made with different drawing conditions.